I would spend more time in HK, and I think it is mentioned on sticky or elsewhere that if you arrive in F, transit in same day, you can get F lounge most.
To be honest though, if you have 15:30 - 22:00 in HK, it may worth to go in-town and have a quick look in the city. only cost you HKD 100 for airport express same day return ticket and HK immigration is efficient.